It is our overall Hypothesis that PTHrP (parathyroid hormone related protein) overexpression in prostate cancer is characterized by the generation of novel, cancer-specific peptides from the three native isoforms of this oncoprotein and that these novel peptides can regulate tumorigenesis and the growth and progression of prostate cancer, especially in the skeleton. Our overall Aim is to identify these peptides and their effects on growth-regulation and tumor progression in order to fully understand the pathobiology of this malignancy. Specific Aim 1. To identify and fully characterize the PTHrP peptides that are derived from the native PTHrP polypeptides in prostate cancer. We shall identify and characterize the PTHrP peptides produced by prostate cancers. This will be accomplished by a multifaceted approach that includes (a) immunochemical procedures like immunoaffinity chromatography, multi-site immunoassays, and immunohistochemistry, including Westerns and (b) biochemical procedures based on mass spectrometry (MS). These methods will be complemented by additional molecular studies of PTHrP. Summary of Expected Results: We expect to identify prostate-specific peptides of PTHrP that mediate effects on growth- and proliferation-related aspects of prostate cancer. In addition to PTHrP's classical peptides, we expect to discover new peptides that can exert their molecular action though novel molecular pathways. Specific Aim 2. To determine how these PTHrP-processed peptides regulate prostate cancer progression in skeletal and other sites. This aim will be accomplished in immunocompromised mice by peptide treatment and by directly implanting into bone and other sites prostate cancer cells that have been genetically engineered for PTHrP expression to respectively manifest the growth regulatory effects of PTHrP and its peptides. Novel imaging procedures will be used to monitor tumor behavior. These models will allow us to study PTHrP's respective effects and molecular interactions that mediate in vivo progression of prostate cancer. Summary of Expected Results: We expect to identify PTHrP peptides that regulate the respective progression, both skeletal and non-skeletal, of prostate cancer in our animal model for this tumor. We expect to inform and focus these in vivo studies based on the corresponding in vitro studies of Aim 1 as well as our Preliminary Results in this area. We expect to identify and elucidate the growth- regulatory domains of PTHrP and its derived peptides in vivo and to thus facilitate exploitation of these mechanisms for the development of diagnostic and therapeutic targets for the tumor. PUBLIC HEALTH RELEVANCE: The importance of our studies of PTHrP (parathyroid hormone related protein) in prostate cancer to Veterans Health is manifest, as this is one of the most common cancers among our patients. Furthermore, our studies may provide basic and clinical information about other common PTHrP-expressing cancers that are relevant to Veterans, including breast, lung, and hematopoetic malignancies like myeloma. The studies that we propose will provide fundamental information about the growth regulating properties of PTHrP in cancer. This basic information can be translated to clinical applications that can be used in the management and diagnosis of these tumors. See also Section 2, Item C of the Research Plan.